Asthma morbidity continues to be a major public health problem among low-income minority children living in urban neighborhoods despite the availability of highly effective controller medications. Major contributors to the disproportionatey high asthma morbidity in this population are exposure to pest allergens (mouse and cockroach) and indoor pollutants (particulate matter (PM) due to second hand smoke and neighborhood PM). Efforts to reduce these exposures using home environmental interventions (EIs) have had only modest effects on measures of asthma symptoms and they have had little effect on reducing acute care visits or on improving lung function which are critical markers of high health care costs and poor long-term outcomes. The limited efficacy of EIs in this high-risk population is likely due to only modest reductions of indoor allergens and pollutants achieved by EIs. Housing mobility programs offer an alternative intervention with the strong potential to achieve large reductions in allergens and pollutants and thereby improve asthma health across a broad range of indicators including acute visits and lung function. We propose to conduct such a study in the context of the Baltimore Mobility Program (BMP), the nation's largest mobility program. We have partnered with BMP, and together have found that among families in BMP who have moved away from Baltimore City, pest allergen and PM exposures are much lower than in the homes of similar children living in Baltimore City. Our preliminary data and findings to date provide strong support for the hypothesis that moving to good quality housing in a better neighborhood through a housing mobility program will result in improvements in asthma outcomes, and that these improvements will be mediated by reductions in exposure to pest allergens and indoor PM. Through prospectively recruiting and following families as they enter into the Baltimore Mobility Program, we seek to address the following specific aims: (1) To determine the effect of moving from a low-income urban neighborhood to good quality housing in a better neighborhood on asthma-related outcomes by comparing outcomes among 5-17 year old children with persistent asthma who move to similar children who do not move, and (2) To estimate the causal effects of reducing indoor pest allergens and PM by moving to better housing on asthma outcomes using principal stratification, a statistical method for causal inference in environmental studies. The proposed study has the potential to have significant implications for the role of housing policy as a tool to address asthma disparities.